I recently bough a condo that is already pre-wired for most things, however I need to run a few additional wires behind the wall where wires already are run (hdmi, etc). Is there a proper way to do this without having to do any damage to the wall?

Search for "wire fishing". And nothing will go diagonal, so to speak. There are techniques to go horizontal and vertical. How far and what obstructions are in the way will determine the difficulty factor.

Search for "wire fishing". And nothing will go diagonal, so to speak. There are techniques to go horizontal and vertical. How far and what obstructions are in the way will determine the difficulty factor.

Search for "wire fishing". And nothing will go diagonal, so to speak. There are techniques to go horizontal and vertical. How far and what obstructions are in the way will determine the difficulty factor.

So diagonal is possible, but it is very difficult?

Anything is possible. It's just a whole lot easier to go vertical then horizontal or horizontal then vertical.

If you only have to go vertical, its very easy. You just cut 2 holes in the wall in between two studs, so you don't need to drill through the studs.

If you also have to go horizontal, you're guaranteed to have to drill through studs and put a hole in your drywall about every 16". Get a long enough drill bit that can make it through your stud by drilling at an angle into the stud (from front to back of stud, front being closest to drywall). Use the fishing tape to pull your wires through the drilled hole to the next drywall hole (which will be next to the next stud).

Patching the holes in the drywall is easy, but getting the paint to match may be more difficult.